ML24072A398

NRR E-mail Capture - for Your Action - Second Round Request for Additional Information (RAI) - Vogtle, Unit 1 - SG Tube Inspection Report - 1R24 (L-2023-LRO-0067)

ML24072A398
Person / Time
Site:	Vogtle
Issue date:	03/12/2024
From:	John Lamb Plant Licensing Branch II
To:	Pournaras D Southern Nuclear Operating Co
References
L-2023-LRO-0067
Download: ML24072A398 (4)

Text

From: John Lamb Sent: Tuesday, March 12, 2024 12:09 PM To: Pournaras, DeLisa S.

Cc: Joyce, Ryan M.

Subject:

For Your Action - Second Round Request for Additional Information (RAI) -

Vogtle, Unit 1 - SG Tube Inspection Report - 1R24 (L-2023-LRO-0067)

DeLisa,

By letter dated September 22, 2023 (Agencywide Documents Access and Management System (ADAMS) Accession No. ML23265A249), as supplemented by letter dated January 22, 2024 (ML24022A222), Southern Nuclear Operating Company (SNC, the licensee) submitted the Steam Generator (SG) Tube Inspection Report for the SG tube inspection performed during the twenty -

fourth refueling outage on Vogtle Electric Generating Plant (Vogtle), Unit 1 (1R24) in accordance with the requirements of Vogtle Technical Specification 5.6.10 as updated by TS Amendment 211 (ML21316A055).

The U.S. Nuclear Regulatory Commission (NRC) staff reviewed the letter dated September 22, 2023, as supplemented by letter dated January 22, 2024, and determined that additional information is needed to complete its review.

On February 16, 2024, the NRC staff provided draft RAI questions to SNC to make sure that the RAI is understandable, the regulatory basis is clear, to ensure there is no proprietary information, and to determine if the information was previously docketed. On February 20, 2024, SNC stated that it would need a clarifying call. On March 11, 2024, a clarifying call was held, and SNC stated that it would provide the RAI response within 45 days from the date of this email.

If you have any questions, please contact me at (301) 415-3100.

Thanks.

John

REQUEST FOR ADDITIONAL INFORMATION (RAI):

By letter dated September 22, 2023 (Agencywide Documents Access and Management System (ADAMS) Accession No. ML23265A249), as supplemented by letter dated January 22, 2024 (ML24022A222), Southern Nuclear Operating Company (SNC, the licensee), submitted information summarizing the results of the spring 2023 steam generator (SG) inspections performed at Vogtle Electric Generating Plant (Vogtle), Unit 1, during the twenty-fourth refueling outage (1R24).

All pressurized water reactors have Technical Specifications (TS) according to § 50.36 of Title 10 of the Code of Federal Regulations that include a SG Program with specific criteria for the structural and leakage integrity, repair, and inspection of SG tubes. Vogtle, Unit 1, TS Section 5.6.10 requires that a report be submitted within 180 days after the initial entry into hot shutdown (MODE 4) following completion of an inspection of the SGs performed in accordance with TS Section 5.5.9, which requires that a SG Program be established and implemented to ensure SG tube integrity is maintained.

To complete its review of the inspection report, the U.S. Nuclear Regulatory Commission (NRC) staff requests the following additional information:

REGULATORY BASIS

In Title 10 of the Code of Federal Regulations (10 CFR), Section 50.36, the Commission established its regulatory requirements related to the content of the TSs. Pursuant to 10 CFR 50.36, Technical Specifications (TSs) are required to include items in the following five specific categories related to station operation: (1) safety limits, limiting safety system settings, and limiting control settings; (2) limiting conditions for operation (LCOs); (3) surveillance requirements; (4) design features; and (5) administrative controls. The rule does not specify the particular requirements to be included in a plants TSs. In 10 CFR 50.36(d)(5), administrative controls are stated to be the provisions relating to organization and management, procedures, recordkeeping, review and audit, and reporting necessary to assure operation of the facility in a safe manner. This also includes the programs established by the licensee and listed in the administrative controls section of the TSs for the licensee to operate the facility in a safe manner. The requirements for SG tube integrity and SG tube reporting on inspections and repair for Vogtle, Unit 1, are in TS 3.4.17, Steam Generator (SG) Tube Integrity, and TS 5.6.10, Steam Generator Tube Inspection Report, respectively. In addition, TS 5.5.9 contains the requirements for the SG Program.

TS 5.5.9(d) states, in part, In addition to meeting the requirements of d.1, d.2, and d.3 below, the inspection scope, inspection methods, and inspection intervals shall be such as to ensure that SG tube integrity is maintained until the next SG inspection. Therefore, NRC staff questions related to a specific SG inspection technique used to detect tube cracking and the techniques probability of detection, which is an input used when projecting future tube integrity, is appropriate.

RAI #1

The SNC response to NRC RAI 1a dated January 22, 2024 (ML24022A222) discussed the site-specific probability of detection (POD) function for maximum flaw depth that was developed using the Electric Power Research Institute (EPRI) model assisted probability of detection (MAPOD) code. The MAPOD process for this technique relies on the regression that is calculated between the voltage amplitude from the +Point' probe and the true depth distribution. This regression is called the Ahat.

a. Discuss why the analyst reporting probability (ARP) provided in Figure 1 (ML24022A222) is appropriate relative to the knowledge gained from previous inspections for circumferential outside diameter stress corrosion cracking (ODSCC) in the hot leg expansion transition region, including previously performed lookback analysis.

b. The eddy current technique (ETSS 21410.1) relies on an eddy current signal phase-to-crack depth relationship, rather than a voltage amplitude-to-crack depth relationship, for sizing ODSCC at this location.

This is presumably due to a better statistical fit between phase angle and crack depth, as compared to voltage amplitude and crack depth.

The NRC staff notes that the maximum depth sizing correlation coefficient shown in ETSS 21410.1 is smaller than the minimum value required for the 95-percent confidence level shown in Table 4-1 in the EPRI Integrity Assessment Guidelines. Please discuss if there is a statistically acceptable relationship between voltage amplitude and crack depth to support the MAPOD Ahat development.

RAI # 2

A summary of circumferential ODSCC at the hot leg expansion transition region from recent tube inspections is provided in the table below:

Refueling Outage ODSCC Indications Average PDA1 (%)

1R21 None N/A 1R22 2 4.6 1R23 8 10.3 1R24 5 20.9

1 - PDA = Percent Degraded Area

The NRC staff notes the average PDA is increasing with time based on the four most recent outages. The 1R24 circumferential indication with the maximum PDA had significant margin to the condition monitoring limit. The data set for ETSS 21410.1, however, shows that the PDA was consistently undersized, particularly for the pulled tube data. According to NRC staff calculations, the average PDA for 1R24 in the table above, when combined with the average amount of PDA undersizing for pulled tubes in ETSS 21410.1, approaches the condition monitoring limit. Please discuss if the PDA trend shown above and the potential for the measured PDA to undersize PDA (ETSS data set) were considered when projecting this degradation mechanism to the next tube inspection.

Hearing Identifier: NRR_DRMA Email Number: 2426

Mail Envelope Properties (MN2PR09MB508466997691FA740CA63BB6FA2B2)

Subject:

For Your Action - Second Round Request for Additional Information (RAI) -

Vogtle, Unit 1 - SG Tube Inspection Report - 1R24 (L-2023-LRO-0067)

Sent Date: 3/12/2024 12:08:57 PM Received Date: 3/12/2024 12:08:00 PM From: John Lamb

Created By: John.Lamb@nrc.gov

Recipients:

"Joyce, Ryan M." <RMJOYCE@southernco.com>

Tracking Status: None "Pournaras, DeLisa S." <DSPOURNA@SOUTHERNCO.COM>

Tracking Status: None

Post Office: MN2PR09MB5084.namprd09.prod.outlook.com

Files Size Date & Time MESSAGE 7169 3/12/2024 12:08:00 PM

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